The shoulder is a ball-and-socket joint that enables you to move your arm in almost any direction. The shoulder is often compared to a golf ball sitting on a tee (Figure 1). The head of the humerus (upper arm bone) is the ball, and a circular concavity (glenoid) in the shoulder bone (scapula) is the socket. A soft-tissue rim called the labrum surrounds and deepens the glenoid, making it more concave. The head of the humerus is coated with articular cartilage, and the shoulder joint has a thin, inner lining that produces an oil-like substance called synovial fluid for smooth movement. The surrounding muscles and tendons provide stability and support.
To learn more about the anatomy of the shoulder and elbow, go to the Interactive Shoulder animation.